1. Field of the Invention
The present invention relates to novel pentablock polymers useful for the administration of biologically active agents or diagnostic agents, especially hydrophilic compounds such as peptides and proteins, and nanoparticles comprising the polymers. The present invention is also directed to controlled release formulations comprising the nanoparticles dispersed in thermosensitive gels. Methods of making the nanoparticles are also described. The present invention is further directed to a method for preparing nanoparticulate compositions comprised of polymers with high levels of bioactive or diagnostic agents and the compositions obtained by such methods.
2. Description of Related Art
Various block polymers are known in the art. For example, Cha et al., U.S. Pat. No. 5,702,717 discloses several triblock polymers, such as the PCL-PEG-PCL and PLA-PEG-PLA triblock polymer comprised of polyethylene glycol (“PEG”) and poly(ε-caprolactone) (“PCL”), and polylactide (“PLA”). See also Lui et al., Thermoreversible gel-sol behavior of biodegradable PCL-PEG-PCL triblock copolymer in aqueous solutions, J. Biomed. Mater. Res. B. Appl. Biomater. January 84 (1) 165-75 (2008). These polymers forming the block polymer are all well-known FDA-approved biodegradable and biocompatible materials. Recently, pentablock polymers having a PGA-PCL-PEG-PCL-PGA or PEG-PCL-PLA-PCL-PEG configuration have been investigated by certain of the present inventors as set forth in Mitra et al., U.S. Pat. No. 8,851,531.